Mixed metal 8-ring small pore molecular sieve catalyst compositions, catalytic articles, systems, and methods

ABSTRACT

Described are compositions and catalytic articles comprising a copper-promoted 8-ring small pore molecular sieve and an iron-promoted 8-ring small pore molecular sieve. The catalytic articles are useful in methods and systems to catalyze the reduction of nitrogen oxides in the presence of a reductant.

PRIORITY

This patent application claims priority to patent application Ser.61/716,073 filed Oct. 19, 2012.

TECHNICAL FIELD

The present invention pertains to the field of selective catalyticreduction catalyst materials. More particularly, embodiments of theinvention relate to mixed metal molecular sieve catalyst compositions,selective catalytic reduction catalytic articles comprising a washcoatcontaining 8-ring small pore molecular sieves, and methods of usingthese catalysts in a variety of processes such as abating pollutants inexhaust gases.

BACKGROUND

Molecular sieves such as zeolites have been used extensively to catalyzea number of chemical reactions in refinery and petrochemical reactions,and catalysis, adsorption, separation, and chromatography. For example,with respect to zeolites, both synthetic and natural zeolites and theiruse in promoting certain reactions, including conversion of methanol toolefins (MTO reactions) and the selective catalytic reduction (SCR) ofnitrogen oxides with a reductant such as ammonia, urea or a hydrocarbonin the presence of oxygen, are well known in the art. Zeolites arecrystalline materials having rather uniform pore sizes which, dependingupon the type of zeolite and the type and amount of cations included inthe zeolite lattice, range from about 3 to 10 Angstroms in diameter.Zeolites having 8-ring pore openings and double-six ring secondarybuilding units, particularly those having cage-like structures haverecently found interest in use as SCR catalysts. A specific type ofzeolite having these properties is chabazite (CHA), which is a smallpore zeolite with 8 member-ring pore openings (˜3.8 Angstroms)accessible through its 3-dimensional porosity. A cage like structureresults from the connection of double six-ring building units by 4rings.

Catalysts employed in the SCR process ideally should be able to retaingood catalytic activity over the wide range of temperature conditions ofuse, for example, 200° C. to 600° C. or higher, under hydrothermalconditions. Hydrothermal conditions are often encountered in practice,such as during the regeneration of a soot filter, a component of theexhaust gas treatment system used for the removal of particles.

Metal-promoted zeolite catalysts including, among others, iron-promotedand copper-promoted zeolite catalysts, for the selective catalyticreduction of nitrogen oxides with ammonia are known. Iron-promotedzeolite beta has been an effective commercial catalyst for the selectivereduction of nitrogen oxides with ammonia. Unfortunately, it has beenfound that under harsh hydrothermal conditions, for example, exhibitedduring the regeneration of a soot filter with temperatures locallyexceeding 700° C., the activity of many metal-promoted zeolites beginsto decline. This decline is often attributed to dealumination of thezeolite and the consequent loss of metal-containing active centerswithin the zeolite.

The synthesis of a zeolite varies according to structure type of thezeolite, but usually, zeolites are synthesized using a structuredirecting agent, sometimes referred to as a template or organictemplate, together with sources of silica and alumina. The structuredirecting agent can be in the form of an organic, i.e.tetraethylammonium hydroxide (TEAOH), or inorganic cation, i.e. Na⁺ orK⁺. During crystallization, the tetrahedral silica-alumina unitsorganize around the SDA to form the desired framework, and the SDA isoften embedded within the pore structure of the zeolite crystals.

Metal-promoted, particularly copper-promoted aluminosilicate zeoliteshaving the CHA structure type and a silica to alumina molar ratiogreater than 1, particularly those having a silica to alumina ratiogreater than or equal to 5, 10, or 15 and less than about 1000, 500,250, 100 and 50 have recently solicited a high degree of interest ascatalysts for the SCR of oxides of nitrogen in lean burning enginesusing nitrogenous reductants. This is because of the wide temperaturewindow coupled with the excellent hydrothermal durability of thesematerials, as described in U.S. Pat. No. 7,601,662. Prior to thediscovery of metal promoted zeolites described in U.S. Pat. No.7,601,662, while the literature had indicated that a large number ofmetal-promoted zeolites had been proposed in the patent and scientificliterature for use as SCR catalysts, each of the proposed materialssuffered from one or both of the following defects: (1) poor conversionof oxides of nitrogen at low temperatures, for example 350° C. andlower; and (2) poor hydrothermal stability marked by a significantdecline in catalytic activity in the conversion of oxides of nitrogen bySCR. Thus, the invention described in U.S. Pat. No. 7,601,662 addresseda compelling, unsolved need to provide a material that would provideconversion of oxides of nitrogen at low temperatures and retention ofSCR catalytic activity after hydrothermal aging at temperatures inexcess of 650° C.

Thus, one of the challenges of meeting current governmental (forexample, Euro 6) NO_(x) regulations is the improvement of lowtemperature performance of the existing Cu-SSZ13 based SCR catalysts.Additionally, light duty diesel (LDD) applications now require fasttransient NO_(x) conversion response at low NH₃ storage levels. Whilecurrent SCR technology has the maximum NO_(x) conversion at its highestNH₃ storage capacity, light duty diesel customers demand the samemaximum NO_(x) conversion from 0.5 g/L to 1 g/L NH₃ storage levels.Accordingly, an SCR catalyst is needed that shows optimal performance atsignificantly lower NH₃ filling level versus Cu-SSZ13.

SUMMARY

A first aspect of the present invention is directed to a selectivecatalytic reduction composition comprising a copper-promoted 8-ringsmall pore molecular sieve and an iron-promoted 8-ring small poremolecular sieve, the composition effective to catalyze the reduction ofnitrogen oxides in the presence of a reductant. In a specificembodiment, the composition is in the form a catalytic article,including a washcoat containing the copper-promoted 8-ring small poremolecular sieve and an iron-promoted 8-ring small pore molecular sieve

In one or more embodiments, the copper-promoted 8-ring small poremolecular sieve is selected from the group consisting of copper-promotedzeolite having a structure type selected from AEI, AFT, AFX, CHA, EAB,ERI, KFI, LEV, SAS, SAT, and SAV. In a specific embodiment, thecopper-promoted 8-ring small pore molecular sieve has the CHA crystalstructure.

In one or more embodiments, the copper-promoted 8-ring small poremolecular sieve has the CHA crystal structure and is selected from analuminosilicate zeolite, a borosilicate, a gallosilicate, a SAPO, anAlPO, a MeAPSO, and a MeAPO.

In one or more embodiments, the copper-promoted 8-ring small poremolecular sieve is selected from the group consisting of copper-promotedSSZ-13, SSZ-62, natural chabazite, zeolite K-G, Linde D, Linde R,LZ-218, LZ-235, LZ-236, ZK-14, SAPO-34, SAPO-44, SAPO-47, and ZYT-6.

In one or more embodiments, the iron-promoted 8-ring small poremolecular sieve has the CHA crystal structure and is selected from thegroup of aluminosilicate zeolite, a borosilicate, a gallosilicate, aSAPO, an AlPO, a MeAPSO, MeAPO. In a specific embodiment, theiron-promoted 8-ring small pore molecular sieve having the CHA structureis an iron-promoted aluminosilicate zeolite having the CHA crystalstructure.

In one or more embodiments, the 8-ring small pore molecular having theCHA structure is an aluminosilicate zeolite having the CHA structure. Ina specific embodiment, the aluminosilicate zeolite having the CHAcrystal structure is selected from SSZ-13 and SSZ-62.

In one or more embodiments, the copper-promoted 8-ring small poremolecular sieve comprises a barium component. In one or moreembodiments, the catalytic article comprises the copper-promoted 8-ringsmall pore molecular sieve and the iron-promoted 8-ring small poremolecular sieve are contained in a single washcoat disposed on asubstrate.

In one or more embodiments, the copper-promoted 8-ring small poremolecular sieve and the iron-promoted 8-ring small pore molecular sieveeach are selected from SSZ-13 and SSZ-62 and are present in a ratio inthe range of 1:1 to 10:1 by weight of the copper-promoted 8-ringmolecular sieve to the iron-promoted 8-ring small pore molecular sieve.In specific embodiments, the range of the copper-promoted 8 ring smallpore molecular sieve to the iron-promoted small more molecular sieve is1:1, 2:1, 3:1, 4:1, 5:1; 6:1; 7:1; 8:1; 9:1 or 10:1 by weight. In one ormore embodiments, the copper-promoted 8-ring small pore molecular sievecomprises a barium component.

In one or more embodiments, the article is effective to catalyze theselective catalytic reduction of nitrogen oxides in the presence of areductant at temperatures between 200° C. to 600° C.

In one or more embodiments, the silica to alumina ratio ofaluminosilicate zeolites is in the range of 10 and 100.

Further embodiments of the invention pertain to a method for selectivelyreducing nitrogen oxides (NOx), the method comprising contacting anexhaust gas stream containing NOx with a catalyst composition comprisinga first 8-ring small pore molecular sieve promoted with copper and asecond 8-ring small pore molecular sieve promoted with iron. The methodmay include any of the above-described variants of the catalyticarticle.

Still a further aspect of the invention pertain to systems for thetreatment of exhaust gas from a lean burn engine containing NOxcomprising the catalytic articles described above and at least one otherexhaust gas treatment component.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a bar chart showing lab reactor NOx conversion of varioussamples, including Cu-CHA and various types of mixtures and zoning ofCu-CHA and Fe-CHA samples.

FIG. 2 is a catalyst system configuration comprising a Diesel OxidationCatalyst (DOC), Catalytic Soot Filter (CSF), Selective CatalyticReduction catalysts (SCRs), and Ammonia Oxidation catalyst (AMOX), usedin Heavy Duty Diesel Federal Test Protocol (HDD FTP) engine test.

FIG. 3 is a graph showing exhaust temperature trace of HDD FTP testequilibrium with total 9 FTP cycles. FTP cycles #1-2 are stabilizationcycles, #3-5 are equilibrium cycles, #6 is a hot active cycle, and #7-9are recovery cycles.

FIG. 4 is a graph showing exhaust temperature trace of HDD FTP testequilibrium cycles #3-5 with and without soaks.

FIG. 5 is a bar chart showing engine data of equilibrium FTP cycles 3-5,NOx conversion for fresh samples of Example 5A with no soaks and freshprior art SCR1.

FIG. 6 is a bar chart showing engine data of equilibrium FTP cycles 3-5,NOx conversion for aged samples of Example 5A with no soaks and agedprior art SCR1.

FIG. 7 is a bar chart showing engine data of equilibrium FTP cycles 3-5,NOx conversion for fresh samples of Example 5A with soaks and freshprior art SCR1

FIG. 8 is a bar chart showing engine data of equilibrium FTP cycles 3-5,NOx conversion for aged samples of Example 5A with soaks and aged priorart SCR1.

FIG. 9 is a bar chart showing engine data, NOx conversion, of FTP cycles#3-9 (equilibrium, active, and recovery cycles) with 0.5 NO2/NOx with nosoaks for fresh samples of Example 5A and fresh prior an SCR2.

FIG. 10 is a bar chart showing engine data, NOx conversion, of FTPcycles #3-9 (equilibrium, active, and recovery cycles) with 0.5 NO₂/NOxwith no soaks for aged samples of Example 5A and aged prior art SCR2.

FIG. 11 is a bar chart showing engine data, brake specific N₂O make, ofFTP cycles #3-9 (equilibrium, active, and recovery cycles) with 0.5NO₂/NOx with no soaks for fresh samples of Example 5A and fresh priorart SCR2.

FIG. 12 is a bar chart showing engine data, brake specific N₂O make, ofFTP cycles #3-9 (equilibrium, active, and recovery cycles) with 0.5NO₂/NOx with no soaks for aged samples of Example 5A and fresh prior artSCR2.

DETAILED DESCRIPTION

Before describing several exemplary embodiments of the invention, it isto be understood that the invention is not limited to the details ofconstruction or process steps set forth in the following description.The invention is capable of other embodiments and of being practiced orbeing carried out in various ways.

Governmental regulations mandate the use of NO_(x) reductiontechnologies for light and heavy-duty vehicles. Selective catalyticreduction (SCR) of NO_(x) using urea is an effective and dominantemission control technology for NO_(x) control. To meet governmentalregulations, an SCR catalyst that has improved low and high temperatureperformance compared to the current Cu-SSZ-13 based benchmark technologyis necessary. Provided is an SCR catalyst having NO_(x) conversionefficiency improvement at low NH₃ storage levels.

Embodiments of the invention are directed to molecular sieves, methodsfor their preparation, catalytic articles including molecular sieves,exhaust gas systems, and methods of abating pollutants from exhaustgases using such molecular sieves.

With respect to the terms used in this disclosure, the followingdefinitions are provided.

As used herein, molecular sieves refer to materials based on anextensive three-dimensional network of oxygen ions containing generallytetrahedral type sites and having a pore distribution. A zeolite is aspecific example of a molecular sieve, further including silicon andaluminum. Reference to a “non-zeolite-support” or “non-zeolitic support”in a catalyst layer refers to a material that is not a molecular sieveor zeolite and that receives precious metals, stabilizers, promoters,binders, and the like through association, dispersion, impregnation, orother suitable methods. Examples of such non-zeolitic supports include,but are not limited to, high surface area refractory metal oxides. Highsurface area refractory metal oxide supports can comprise an activatedcompound selected from the group consisting of alumina, zirconia,silica, titania, silica-alumina, zirconia-alumina, titania-alumina,lanthana-alumina, lanthana-zirconia-alumina, baria-alumina,baria-lanthana-alumina, baria-lanthana-neodymia-alumina,zirconia-silica, titania-silica, and zirconia-titania.

As used herein, the term “catalyst” refers to a material that promotes areaction. As used herein, the phrase “catalyst composition” refers to acombination of two or more catalysts, or example a combination of aniron-promoted molecular sieve and a copper-promoted molecular sieve. Thecatalyst composition may be in the form of a washcoat in which the twomolecular sieves are mixed together.

As used herein, the term “carrier” refers to a support that carries orsupports a catalytic species. For example, refractory metal oxideparticles may be a carrier for platinum group metal catalytic species.

As used herein, the term “substrate” refers to the monolithic materialonto which the carrier is placed, typically in the form of a washcoatcontaining a plurality of carriers having catalytic species thereon. Awashcoat is formed by preparing a slurry containing a specified solidscontent (e.g., 30-90% by weight) of carriers in a liquid vehicle, whichis then coated onto a substrate and dried to provide a washcoat layer.

As used herein, the term “washcoat” has its usual meaning in the art ofa thin, adherent coating of a catalytic or other material applied to asubstrate carrier material, such as a honeycomb-type carrier member,which is sufficiently porous to permit the passage of the gas streambeing treated.

“Catalytic article” refers to an element that is used to promote adesired reaction. For example, a catalytic article may comprise awashcoat containing catalytic species on a substrate.

In one or more embodiments, the substrate is a ceramic or metal having ahoneycomb structure. Any suitable substrate may be employed, such as amonolithic substrate of the type having fine, parallel gas flow passagesextending there through from an inlet or an outlet face of the substratesuch that passages are open to fluid flow there through. The passages,which are essentially straight paths from their fluid inlet to theirfluid outlet, are defined by walls on which the catalytic material iscoated as a washcoat so that the gases flowing through the passagescontact the catalytic material. The flow passages of the monolithicsubstrate are thin-walled channels, which can be of any suitablecross-sectional shape and size such as trapezoidal, rectangular, square,sinusoidal, hexagonal, oval, circular, etc. Such structures may containfrom about 60 to about 900 or more gas inlet openings (i.e. cells) persquare inch of cross section.

The ceramic substrate may be made of any suitable refractory material,e.g. cordierite, cordierite-α-alumina, silicon nitride, zircon mullite,spodumene, alumina-silica-magnesia, zircon silicate, sillimanite, amagnesium silicate, zircon, petalite, α-alumina, an aluminosilicate andthe like.

The substrates useful for the catalyst carriers of embodiments of thepresent invention may also be metallic in nature and be composed of oneor more metals or metal alloys. The metallic substrates may be employedin various shapes such as pellets, corrugated sheet or monolithic form.Specific examples of metallic substrates include the heat-resistant,base-metal alloys, especially those in which iron is a substantial ormajor component. Such alloys may contain one or more of nickel,chromium, and aluminum, and the total of these metals may advantageouslycomprise at least about 15 wt. % of the alloy, for instance, about 10 to25 wt. % chromium, about 1 to 8 wt. % of aluminum, and about 0 to 20 wt.% of nickel.

One or more embodiments are directed to catalyst compositions comprisingan iron-promoted 8-ring small pore molecular sieve and a copper-promoted8-ring small pore molecular sieve. In specific embodiments, the catalystcomposition is in the form of a washcoat which provides a catalyticarticle. In one embodiment, a catalytic article comprises a washcoatcontaining both a copper-promoted 8-ring small pore molecular sieve andan iron-promoted 8-ring small pore molecular sieve. In specificembodiments the washcoat is on a substrate.

“Rich gaseous streams” including rich exhaust streams mean gas streamsthat have a λ<1.0.

“Rich periods” refer to periods of exhaust treatment where the exhaustgas composition is rich, i.e., has a λ<1.0.

“Rare earth metal components” refer to one or more oxides of thelanthanum series defined in the Periodic Table of Elements, includinglanthanum, cerium, praseodymium and neodymium. Rare earth metalcomponents can include at least one rare earth metal selected from Ce,Pr, Nd, Eu, Nb, Sm, Yb, and La.

“Alkaline earth component” refers to one or more chemical elementsdefined in the Periodic Table of Elements, including beryllium (Be),magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium(Ra).

“Alkali metal component” refers to one or more chemical elements definedin the Periodic Table of Elements, including lithium (Li), sodium (Na),potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr).

The catalytic articles are effective to catalyze the reduction ofnitrogen oxides in the presence of a reductant. The molecular sieveshave 8-ring pore openings and double-six ring secondary building units,for example, those having the following structure types: AEI, AFT, AFX,CHA, EAB, ERI, KFI, LEV, SAS, SAT, and SAV. According to one or moreembodiments, it will be appreciated that by defining the molecularsieves by their structure type, it is intended to include the structuretype and any and all isotypic framework materials such as SAPO, AlPO andMeAPO materials having the same structure type.

In more specific, embodiments, reference to an aluminosilicate zeolitestructure type limits the material to molecular sieves that do notinclude phosphorus or other metals substituted in the framework. Ofcourse, aluminosilicate zeolites may be subsequently ion-exchanged withone or more promoter metals such as iron, copper, cobalt, nickel, ceriumor platinum group metals. However, to be clear, as used herein,“aluminosilicate zeolite” excludes aluminophosphate materials such asSAPO AlPO, and MeAPO materials, and the broader term “zeolite” isintended to include aluminosilicates and aluminophosphates.

Three different catalytic article designs were prepared using Cu-SSZ-13and Fe-SSZ-13. The designs included layered, zoned, and a uniformmixture in a 2:1 ratio of Cu-SSZ-13:Fe-SSZ-13. The uniform mixturecatalytic article showed the highest performance at 200° C. and 600° C.

In general, the SCR catalytic article based on a copper-promoted 8-ringsmall pore molecular sieve and an iron-promoted 8-ring small poremolecular sieve should exhibit equivalent or better NO_(x) conversionactivity with Cu-SSZ13 catalytic articles. In general, the catalyticarticle should exhibit both good low temperature NO_(x) conversionactivity (NO_(x) conversion>50% at 200° C.) and good high temperatureNO_(x) conversion activity (NO_(x) conversion>70% at 450° C.). TheNO_(x) activity is measured under steady state conditions at maximumNH₃-slip conditions in a gas mixture of 500 ppm NO, 500 ppm NH₃, 10% O₂,5% H₂O, balance N₂ at a volume-based space velocity of 80,000 h⁻¹.

In one or more embodiments, the catalytic article is a uniform mixtureof a copper-promoted 8-ring small pore molecular sieve and aniron-promoted 8-ring small pore molecular sieve having the CHA crystalstructure. In specific embodiments, the copper-promoted 8-ring smallpore molecular sieve and the iron-promoted 8-ring small pore molecularsieve having the CHA crystal structure are present in a ratio of in therange of 1:1 to 10:1 by weight of copper promoted to iron promotedmolecular sieve, including ratios of 1:1; 2:1; 3:1; 4:1; 5:1; 6:1; 7:1;8:1; 9:1 and 10:1 of the copper promoted 8-ring small pore molecularsieve material to the iron-promoted 8-ring small pore molecular sievematerial.

As used herein, the term “Na⁺-form of chabazite” refers to the calcinedform of this zeolite without any ion exchange. In this form, the zeolitegenerally contains a mixture of Na⁺ and H⁺ cations in the exchangesites. The fraction of sites occupied by Na⁺ cations varies depending onthe specific zeolite batch and recipe.

A molecular sieve can be zeolitic—zeolites—or non-zeolitic, and zeoliticand non-zeolitic molecular sieves can have the chabazite crystalstructure, which is also referred to as the CHA structure by theInternational Zeolite Association. Zeolitic chabazite include anaturally occurring tectosilicate mineral of a zeolite group withapproximate formula: (Ca,Na₂,K₂,Mg)Al₂Si₄O₁₂.6H₂O (e.g., hydratedcalcium aluminum silicate). Three synthetic forms of zeolitic chabaziteare described in “Zeolite Molecular Sieves,” by D. W. Breck, publishedin 1973 by John Wiley & Sons, which is hereby incorporated by reference.The three synthetic forms reported by Breck are Zeolite K-G, describedin J. Chem. Soc., p. 2822 (1956), Barrer et al; Zeolite D, described inBritish Patent No. 868,846 (1961); and Zeolite R, described in U.S. Pat.No. 3,030,181, which are hereby incorporated by reference. Synthesis ofanother synthetic form of zeolitic chabazite, SSZ-13, is described inU.S. Pat. No. 4,544,538, which is hereby incorporated by reference.Synthesis of a synthetic form of a non-zeolitic molecular sieve havingthe chabazite crystal structure, silicoaluminophosphate 34 (SAPO-34), isdescribed in U.S. Pat. No. 4,440,871 and U.S. Pat. No. 7,264,789, whichare hereby incorporated by reference. A method of making yet anothersynthetic non-zeolitic molecular sieve having chabazite structure,SAPO-44, is described in U.S. Pat. No. 6,162,415, which is herebyincorporated by reference.

In one or more embodiments, the copper-promoted 8-ring small poremolecular sieve is selected from the group consisting of AEI, AFT, AFX,CHA, EAB, ERI, KFI, LEV, SAS, SAT, and SAV. In a more specificembodiment, the copper-promoted 8-ring small pore molecular sieve caninclude all aluminosilicate, borosilicate, gallosilicate, MeAPSO, andMeAPO compositions. These include, but are not limited to SSZ-13,SSZ-62, natural chabazite, zeolite K-G, Linde D. Linde R, LZ-218,LZ-235. LZ-236, ZK-14, SAPO-34, SAPO-44, SAPO-47, ZYT-6, CuSAPO-34,CuSAPO-44, and CuSAPO-47. However, in specific embodiments, the 8-ringsmall pore molecular sieve will have the aluminosilicate composition,such as SSZ-13 and SSZ-62, which would exclude borosilicate,gallosilicate, MeAPSO, SAPO and MeAPO compositions.

In one or more embodiments, the iron-promoted 8-ring small poremolecular sieve has the CHA crystal structure and is selected from thegroup is consisting of aluminosilicate zeolite having the CHA crystalstructure, SAPO, AlPO, and MeAPO. In particular, the 8-ring small poremolecular sieve having the CHA crystal structure is an aluminosilicatezeolite having the CHA crystal structure. In a specific embodiment, the8-ring small pore molecular sieve having the CHA crystal structure willhave an aluminosilicate composition, such as SSZ-13 and SSZ-62.

Wt % Iron:

The Fe content of the 8-ring small pore molecular sieve promoted withiron, calculated as Fe₂O₃, in specific embodiments is at least about 1.5wt.-%, even more specifically at least about 2 wt.-% and in even morespecific embodiments at least about 2.5 wt.-%, reported on avolatile-free basis. In even more specific embodiments, the Fe contentof the 8-ring small pore molecular sieve promoted with copper,calculated as CuO, is in the range of up to about 10 wt.-%, morespecifically of up to about 9 wt.-%, 8 wt.-%, 7 wt.-%, 6 wt.-%, 5 wt.-%,4 wt.-% and even more specifically of up to about 3 wt.-%, in each casebased on the total weight of the calcined molecular sieve with the CHAstructure reported on a volatile free basis. Therefore, in specificembodiments, ranges of the 8-ring small pore molecular sieve promotedwith copper, calculated as Fe₂O₃, are from about 1 to about 10 wt.-%,more specifically from about 3 to about 10 wt.-%, and even morespecifically from about 5 to about 10 wt.-%, and even more specificallyfrom about 6 to about 10 wt.-%, in each case reported on a volatile-freebasis.

Wt % Copper:

The Cu content of the 8-ring small pore molecular sieve promoted withcopper, calculated as CuO, in specific embodiments is at least about 1.5wt.-%, even more specifically at least about 2 wt.-% and in even morespecific embodiments at least about 2.5 wt.-%, reported on avolatile-free basis. In even more specific embodiments, the Cu contentof the 8-ring small pore molecular sieve promoted with copper,calculated as CuO, is in the range of up to about 5 wt.-%, morespecifically of up to about 4 wt.-%, and even more specifically of up toabout 3.5 wt.-%, in each case based on the total weight of the calcinedmolecular sieve with the CHA structure reported on a volatile freebasis. Therefore, in specific embodiments, ranges of the 8-ring smallpore molecular sieve promoted with copper, calculated as CuO, are fromabout 2 to about 5 wt.-%, more specifically from about 2 to about 4wt.-%, and even more specifically from about 2.5 to about 3.5 wt.-%, andeven more specifically from about 2.75 to about 3.5 wt.-%, in each casereported on a volatile-free basis.

Additionally, the copper-promoted 8-ring small pore molecular sieve cancomprise an alkaline earth or alkali metal component. In one or moreembodiments, the alkaline earth or alkali earth component is selectedfrom barium, magnesium, beryllium, calcium, strontium, radium, andcombinations thereof. In a specific embodiment, the alkaline earth oralkali metal component is selected from barium, magnesium, calcium, andcombinations thereof. In a more specific embodiment, the alkaline earthor alkali metal component is barium.

In one or more embodiments, the alkaline earth or alkali metal componentloading is less than 5% by weight. In a specific embodiment, thealkaline earth or alkali metal component loading is less than 2.5% byweight. In a more specific embodiment, the alkaline earth or alkalimetal component loading is less than 0.5% by weight. In a very specificembodiment, the copper-promoted 8-ring small pore molecular sievecomprises barium that is loaded in an amount of 0.5% by weight.

In one or more embodiments, the copper is exchanged into an 8-ring smallpore molecular sieve. In one or more embodiments, the iron is exchangedinto a separate 8-ring small pore molecular sieve. The copper-exchangedmolecular sieve and iron-exchanged molecular sieve can be the same typeof molecular sieve, for example, Cu-SSZ-13 and Fe-SSZ-13 may be placedinto a single washcoat by mixing slurries of Cu-SSZ-13 and Fe-SSZ-13obtained from separate exchange processes. In other embodiments, theCu-exchanged molecular sieve and the Fe-exchanged molecular sieve may bedifferent. By “different”, the molecular sieve may have differentproperties such as silica to alumina mole ratio or other properties suchas crystallite size. For example, a composition in accordance withembodiments of the invention may comprise Cu-SSZ-13 and Fe-SAPO-34 in asingle washcoat, or Fe-SSZ-13 and Cu-SAPO-34 in a single washcoat.

In specific embodiments, the 8-ring small pore molecular sieve promotedwith copper and the 8-ring small pore molecular sieve promoted with ironhave a mole ratio of silica to alumina greater than about 15, even morespecifically greater than about 20. In specific embodiments, the 8-ringsmall pore molecular sieve promoted with copper and the 8-ring smallpore molecular sieve promoted with iron has a mole ratio of silica toalumina in the range from about 20 to about 256, more specifically inthe range from about 25 to about 40.

In specific embodiments, the atomic ratio of copper to aluminum exceedsabout 0.25. In more specific embodiments, the ratio of copper toaluminum is from about 0.25 to about 1, even more specifically fromabout 0.25 to about 0.5. In even more specific embodiments, the ratio ofcopper to aluminum is from about 0.3 to about 0.4.

SCR Activity:

In specific embodiments, the catalyst compositions and catalyticarticles exhibit an aged NO_(x) conversion at 200° C. of at least 50%measured at a gas hourly space velocity of 80000 h⁻¹. In specificembodiments the catalyst compositions and catalytic articles exhibit anaged NO_(x) conversion at 450° C. of at least 70% measured at a gashourly space velocity of 80000 h⁻¹. More specifically the aged NO_(x)conversion at 200° C. is at least 55% and at 450° C. at least 75%, evenmore specifically the aged NO_(x) conversion at 200° C. is at least 60%and at 450° C.′ at least 80%, measured at a gas hourly volume-basedspace velocity of 80000 h⁻¹ under steady state conditions at maximumNH₃-slip conditions in a gas mixture of 500 ppm NO, 500 ppm NH₃, 10% O₂,5% H₂O, balance N₂. The cores were hydrothermally aged in a tube furnacein a gas flow containing 10% H₂O, 10% O₂, balance N₂ at a space velocityof 4,000 h⁻¹ for 6 h at 85° C. The SCR activity measurement has beendemonstrated in the literature, for example WO 2008/106519.

Sodium Content:

In specific embodiments, the 8-ring small pore molecular sieve promotedwith copper and the 8-ring small pore molecular sieve promoted with ironeach have a sodium content (reported as Na₂O on a volatile free basis)of below 2 wt.-%, based on the total weight of the calcined molecularsieve. In more specific embodiments, sodium content is below 1 wt.-%,even more specifically below 2500 ppm.

Na:Al:

In specific embodiments, the 8-ring small pore molecular sieve promotedwith copper and the 8-ring small pore molecular sieve promoted with ironeach have an atomic sodium to aluminum ratio of less than 0.7. In morespecific embodiments, the atomic sodium to aluminum ratio is less than0.35, even more specifically less than 0.007, even more specificallyless than 0.03 and even more specifically less than 0.02.

Na:Cu:

In specific embodiments, the 8-ring small pore molecular sieve promotedwith copper and the 8-ring small pore molecular sieve promoted with ironeach have an atomic copper to sodium ratio of greater than 0.5. In morespecific embodiments, the atomic copper to sodium ratio of greater than1, even more specifically greater than 10, even more specificallygreater than 50.

Conventional Zeolite Synthesis of CHA-Type Zeolites

In what may be referred to as a conventional synthesis of an 8-ringsmall pore molecular sieve (for example having the CHA structure), asource of silica, a source of alumina, and a structure directing agentare mixed under alkaline aqueous conditions. Typical silica sourcesinclude various types of fumed silica, precipitated silica, andcolloidal silica, as well as silicon alkoxides. Typical alumina sourcesinclude boehmites, pseudo-boehmites, aluminum hydroxides, aluminum saltssuch as aluminum sulfite or sodium aluminate, and aluminum alkoxides.Sodium hydroxide is typically added to the reaction mixture. A typicalstructure directing agent for this synthesis is adamantyltrimethylammonium hydroxide, although other amines and/or quaternary ammoniumsalts may be substituted or added to the latter directing agent. Thereaction mixture is heated in a pressure vessel with stirring to yieldthe crystalline SSZ-13 product. Typical reaction temperatures are in therange of 100 and 200° C., and in specific embodiments between 135 and170° C. Typical reaction times are between 1 hr and 30 days, and inspecific embodiments, between 10 hours and 3 days.

At the conclusion of the reaction, optionally the pH is adjusted tobetween 6 and 10, and in specific embodiments, between 7 and 7.5, andthe product is filtered and washed with water. Any acid can be used forpH adjustment, and in specific embodiments nitric acid is used.Alternatively, the product may be centrifuged. Organic additives may beused to help with the handling and isolation of the solid product.Spray-drying is an optional step in the processing of the product. Thesolid product is thermally treated in air or nitrogen. Alternatively,each gas treatment can be applied in various sequences, or mixtures ofgases can be applied. Typical calcination temperatures are in the 400°C. to 850° C. range.

Optionally NH₄-Exchange to Form NH₄-Chabazite:

Optionally, the obtained alkali metal molecular sieve is NH₄-exchangedto form NH₄-Chabazite. The NH₄-ion exchange can be carried out accordingto various techniques known in the art, for example Bleken, F.; Bjorgen,M.; Palumbo, L.; Bordiga, S.; Svelle, S.; Lillerud, K.-P.; and Olsbye,U. Topics in Catalysis 52, (2009), 218-228.

Synthesis of CHA-Type Zeolites According to Embodiments of the Invention

According to one or more embodiments, methods for the synthesis ofselective catalytic reduction catalytic articles comprising a washcoatcontaining a copper-promoted 8-ring small pore molecular sieve and aniron-promoted 8-ring small pore molecular sieve are provided. Inspecific embodiments, the catalytic article comprises a washcoatcontaining copper-promoted SSZ-13 and iron-promoted SAPO. In otherembodiments, both the copper-promoted 8-ring small pore molecular sieveand the iron-promoted 8-ring small pore molecular sieve are selectedfrom SSZ-13 and/or SSZ-62. The synthesis of copper-promoted CHA-typezeolites and iron-promoted CHA-type zeolites, particularly CHA-typealuminosilicate zeolites such as SSZ-13 and SSZ-62 are provided.

Generally, barium can be incorporated into a copper-promoted 8-ringsmall pore molecular sieve (e.g. Cu-CHA) by crushing, then calcining thedirect exchanged Cu-CHA filter cake at 600° C. for 4 hours. A slurry isprepared to 45% target solids, followed by the addition of 2.5% ZrOAcbinder based or, zeolite solids. The slurry is milled to D₉₀% of 7-10microns. A solution of Ba(OAc)₂ (30 mL) is added dropwise to the aqueousslurry of the copper-promoted 8-ring small pore molecular sieve. The pHis adjusted to 4.5 using 15% ammonium hydroxide solution.

Generally, iron is incorporated into the molecular sieve through anFe-ion exchange at 60° C. for 2 hours at pH 4. The mixture is thenwashed with deionized water, filtered, and vacuum/air dried. A slurry isprepared of Fe-CHA to 45% target solids, and 5% ZrOAc binder is addedbased on the zeolite solids. The slurry is mixed well and then milled toD₉₀% of 7-10 microns.

The Fe-CHA slurry is then added to the Ba—Cu-CHA slurry in a ratio of2:1 Cu-CHA:Fe-CHA. The slurries are mixed well, and the pH is adjustedto 4.5 with 15% ammonium hydroxide solution. The mixture is then coatedonto to substrates to a washcoat loading of 3 g/in³. The washcoat isdried under air at 130° C. for 5 min. A second coat is then applied.After the final coating, the substrate is calcined at 450° C. for 1hour.

BET:

In specific embodiments, the 8-ring small pore molecular sieve promotedwith copper and the 8-ring small pore molecular sieve promoted with ironexhibits a BET surface area, determined according to DIN 66131, of atleast about 400 m²/g, more specifically of at least about 550 m²/g, evermore specifically of at about 650 m²/g. In specific embodiments, the8-ring small pore molecular sieve promoted with copper and the 8-ringsmall pore molecular sieve promoted with iron exhibit a BET surface areain the range from about 400 to about 750 m²/g, more specifically fromabout 500 to about 750 m²/g.

In specific embodiments, the crystallites of the calcined the 8-ringsmall pore molecular sieve promoted with copper and the 8-ring smallpore molecular sieve promoted with iron have a mean length in the rangeof from 10 nanometers to 100 micrometers, specifically in the range offrom 50 nanometers to 5 micrometers, more specifically in the range of50 nanometers to 500 nanometers as determined via SEM. In more specificembodiments, the molecular sieve crystallites have a mean length greaterthan 0.5 microns or 1 micron, and less than 5 microns.

Shape:

The compositions according to embodiments of the invention may beprovided in the form of a powder or a sprayed material obtained fromabove-described separation techniques, e.g. decantation, filtration,centrifugation, or spraying. In general, the powder or sprayed materialcan be shaped without any other compounds, e.g. by suitable compacting,to obtain moldings of a desired geometry, e.g. tablets, cylinders,spheres, or the like. By way of example, the powder or sprayed materialis admixed with or coated by suitable modifiers well known in the art.By way of example, modifiers such as silica, alumina, zeolites orrefractory binders (for example a zirconium precursor) may be used. Thepowder or the sprayed material, optionally after admixing or coating bysuitable modifiers, may be formed into a slurry, for example with water,which is deposited upon a suitable refractory carrier (for example WO2008/106519).

The compositions containing 8-ring small pore molecular sieve promotedwith copper and the 8-ring small pore molecular sieve promoted with ironaccording to embodiments of the invention may also be provided in theform of extrudates, pellets, tablets or particles of any other suitableshape, for use as a packed bed of particulate catalyst, or as shapedpieces such as plates, saddles, tubes, or the like.

In specific embodiments, the molecular sieves are substantiallycomprised of alumina and silica and have a silica to alumina ratio inthe range of about 1 to 1000, and in specific embodiments from 1 to 500,and in more specific embodiments from 5 to 300, 5 to 200, 5 to 100, 10to 90, 10 to 80, 10 to 70, 10 to 60, 10 to 50, 10 to 40, 10 to 35 and 10to 30 are within the scope of the invention. In specific embodiments,the molecular sieves are copper-promoted SSZ-13 and/or copper-promotedSSZ-62, and iron-promoted SAPO.

Moreover, embodiments of the invention relates to a method of catalyzinga chemical reaction wherein the composition containing an 8-ring smallpore molecular sieve promoted with copper and an 8-ring small poremolecular sieve promoted with iron according to embodiments of theinvention is employed as catalytically active material. As discussedabove, the composition is used to provide a catalytic article, forexample, a washcoat disposed on substrate such as a honeycomb substrate.

Among others, said compositions and catalytic articles may be employedto catalyze the selective reduction (SCR) of nitrogen oxides (NO_(x));for the oxidation of NH₃, in particular for the oxidation of NH₃ slip indiesel systems; for the decomposition of N₂O; for soot oxidation; foremission control in Advanced Emission Systems such as Homogeneous ChargeCompression Ignition (HCCl) engines; as additive in fluid catalyticcracking (FCC) processes; to catalyze organic conversion reactions; orin “stationary source” processes. For applications in oxidationreactions, in specific embodiments an additional precious metalcomponent is added to the copper chabazite (e.g. Pd, Pt).

Therefore, embodiments of the invention also relate to a method forselectively reducing nitrogen oxides (NO_(x)) by contacting a streamcontaining NO_(x) with a composition or catalytic article containing the8-ring small pore molecular sieve promoted with copper and the 8-ringsmall pore molecular sieve promoted with iron according to embodimentsof the invention under suitable reducing conditions; to a method ofoxidizing NH₃, in particular of oxidizing NH₃ slip in diesel systems, bycontacting a stream containing NH₃ with a composition or catalyticarticle comprising an 8-ring small pore molecular sieve promoted withcopper and an 8-ring small pore molecular sieve promoted with ironaccording to embodiments of the invention under suitable oxidizingconditions; to a method of decomposing of N₂O by contacting a streamcontaining N₂O with a composition or catalytic article comprising an8-ring small pore molecular sieve promoted with copper and the 8-ringsmall pore molecular sieve promoted with iron according to embodimentsof the invention under suitable decomposition conditions; to a method ofcontrolling emissions in Advanced Emission Systems such as HomogeneousCharge Compression Ignition (HCCl) engines by contacting an emissionstream with a composition or catalytic article comprising a washcoatcontaining both an 8-ring small pore molecular sieve promoted withcopper and the 8-ring small pore molecular sieve promoted with ironaccording to embodiments of the invention under suitable conditions; toa fluid catalytic cracking FCC process wherein the composition orcatalytic article comprising an 8-ring small pore molecular sievepromoted with copper and the 8-ring small pore molecular sieve promotedwith iron is employed as additive; to a method of converting an organiccompound by contacting said compound with a composition or catalyticarticle comprising an 8-ring small pore molecular sieve promoted withcopper and the 8-ring small pore molecular sieve promoted with ironaccording to embodiments of the invention under suitable conversionconditions; to a “stationary source” process wherein a composition orcatalytic article containing the 8-ring small pore molecular sievepromoted with copper and the 8-ring small pore molecular sieve promotedwith iron is employed according to embodiments of the invention.

In particular, the selective reduction of nitrogen oxides is achievedusing an composition or article containing both an 8-ring small poremolecular sieve promoted with copper and the 8-ring small pore molecularsieve promoted with iron according to embodiments of the invention. Thecatalytic article is contacted with exhaust gas in the presence ofammonia or urea. While ammonia is the reducing agent of choice forstationary power plants, urea is the reducing agent of choice for mobileSCR systems. Typically, the SCR system is integrated in the exhaust gastreatment system of a vehicle and, also typically, contains thefollowing main components: selective catalytic reduction catalyticarticle containing an 8-ring small pore molecular sieve promoted withcopper and an 8-ring small pore molecular sieve promoted with ironaccording to embodiments of the invention; a urea storage tank; a ureapump; a urea dosing system; a urea injector/nozzle; and a respectivecontrol unit.

Method of Reducing NO_(x):

Therefore, embodiments of the invention also relates to a method forselectively reducing nitrogen oxides (NO_(x)), wherein a gaseous streamcontaining nitrogen oxides (NO_(x)), for example, exhaust gas formed inan industrial process or operation, and in specific embodiments alsocontaining ammonia and/or urea, is contacted with a composition or aselective catalytic reduction catalytic article containing the 8-ringsmall pore molecular sieve promoted with copper and the 8-ring smallpore molecular sieve promoted with iron according to embodiments of theinvention.

The term nitrogen oxides, NO_(x), as used in the context of embodimentsof the invention designates the oxides of nitrogen, especiallydinitrogen oxide (N₂O), nitrogen monoxide (NO), dinitrogen trioxide(N₂O₃), nitrogen dioxide (NO₂), dinitrogen tetroxide (N₂O₄), dinitrogenpentoxide (N₂O₅), nitrogen peroxide (NO₃).

The nitrogen oxides which are reduced using a composition or catalyticarticle comprising containing the 8-ring small pore molecular sievepromoted with copper and the 8-ring small pore molecular sieve promotedwith iron according to embodiments of the invention or an 8-ring smallpore molecular sieve promoted with copper and the 8-ring small poremolecular sieve promoted with iron obtainable or obtained according toembodiments of the invention may be obtained by any process, e.g. as awaste gas stream. Among others, waste gas streams as obtained inprocesses for producing adipic acid, nitric acid, hydroxylaminederivatives, caprolactame, glyoxal, methyl-glyoxal, glyoxylic acid or inprocesses for burning nitrogeneous materials may be mentioned.

In specific embodiments, a composition or catalytic article containingthe 8-ring small pore molecular sieve promoted with copper and the8-ring small pore molecular sieve promoted with iron is used for removalof nitrogen oxides (NO_(x)) from exhaust gases of internal combustionengines, in particular diesel engines, which operate at combustionconditions with air in excess of that required for stoichiometriccombustion, i.e., lean.

Therefore, embodiments of the invention also relate to a method forremoving nitrogen oxides (NO_(x)) from exhaust gases of internalcombustion engines, in particular diesel engines, which operate atcombustion conditions with air in excess of that required forstoichiometric combustion, i.e., at lean conditions, wherein acomposition or catalytic article containing both the 8-ring small poremolecular sieve promoted with copper and the 8-ring small pore molecularsieve promoted with iron according to embodiments of the invention or an8-ring small pore molecular sieve promoted with copper and the 8-ringsmall pore molecular sieve promoted with iron is employed.

Exhaust Gas Treatment System:

Embodiments of the invention relate to an exhaust gas treatment systemcomprising an exhaust gas stream optionally containing a reductant suchas ammonia, urea and/or hydrocarbon, and in specific embodiments,ammonia and/or urea, and a selective catalytic reduction catalyticarticle containing the 8-ring small pore molecular sieve promoted withcopper and the 8-ring small pore molecular sieve promoted with iron,disposed on a substrate, and a second exhaust gas treatment component,for example, a soot filter and a diesel oxidation catalyst.

The soot filter, catalyzed or non-catalyzed, may be upstream ordownstream of said catalytic article. The diesel oxidation catalyst inspecific embodiments is located upstream of said catalytic article. Inspecific embodiments, said diesel oxidation catalyst and said catalyzedsoot filter are upstream from said catalytic article.

In specific embodiments, the exhaust is conveyed from the diesel engineto a position downstream in the exhaust system, and in more specificembodiments, containing NO_(x), where a reductant is added and theexhaust stream with the added reductant is conveyed to said catalyticarticle.

For example, a catalyzed soot filter, a diesel oxidation catalyst and areductant are described in WO 2008/106519 which is incorporated byreference. In specific embodiments, the soot filter comprises awall-flow filter substrate, where the channels are alternately blocked,allowing a gaseous stream entering the channels from one direction(inlet direction), to flow through the channel walls and exit from thechannels from the other direction (outlet direction).

An ammonia oxidation catalyst may be provided downstream of thecatalytic article to remove any slipped ammonia from the system. Inspecific embodiments, the AMOX catalyst may comprise a platinum groupmetal such as platinum, palladium, rhodium or combinations thereof. Inmore specific embodiment, the AMOX catalyst can include a washcoatcontaining both the 8-ring small pore molecular sieve promoted withcopper and the 8-ring small pore molecular sieve promoted with iron.

Such AMOX catalysts are useful in exhaust gas treatment systemsincluding an SCR catalyst. As discussed in commonly assigned U.S. Pat.No. 5,516,497, the entire content of which is incorporated herein byreference, a gaseous stream containing oxygen, nitrogen oxides andammonia can be sequentially passed through first and second catalysts,the first catalyst favoring reduction of nitrogen oxides and the secondcatalyst favoring the oxidation or other decomposition of excessammonia. As described in U.S. Pat. No. 5,516,497, the first catalystscan be a SCR catalyst comprising a zeolite and the second catalyst canbe an AMOX catalyst comprising a zeolite.

AMOX and/or SCR catalyst composition can be coated on the flow throughor wall-flow filter. If a wall flow substrate is utilized, the resultingsystem will be able to remove particulate matter along with gaseouspollutants. The wall-flow filter substrate can be made from materialscommonly known in the art, such as cordierite, aluminum titanate orsilicon carbide. It will be understood that the loading of the catalyticcomposition on a wall flow substrate will depend on substrate propertiessuch as porosity and wall thickness, and typically will be lower thanloading on a flow through substrate.

Ion Exchange of Metal:

The 8-ring small pore molecular sieve promoted with iron or promotedwith copper may be promoted with other metals. Suitable metals include,but are not limited to cobalt, nickel, cerium, platinum, palladium,rhodium and combinations thereof. The metal can be exchanged aftermanufacture of the zeolite. According to one or more embodiments, atleast a portion of the metal can be included in the tailored colloidsuch that the tailored colloid contains the structure directing agent, asilica source, and alumina source and a metal ion (e.g., copper) source.

For additional promotion of SCR of oxides of nitrogen, a suitablealkaline earth or alkali metal is exchanged into the copper promotedmolecular sieve material. Suitable alkaline earth or alkali metalsinclude, but are not limited to, barium, magnesium, beryllium, calcium,strontium, radium, and combinations thereof. In specific embodiments,the alkaline earth or alkali metal component is selected from barium,magnesium, calcium and combinations thereof. In very specificembodiments, barium is exchanged into the copper promoted molecularsieve. The metal can be exchanged after the manufacture of the molecularsieve.

Copper-Exchange or Iron-Exchange into to Alkali Metal or NH₄-Chabaziteto Form Metal-Chabazite:

Copper or iron is ion exchanged into alkali metal or NH4 8 ring smallpore molecular sieves. In specific embodiments, copper or iron is ionexchanged into alkali metal or NH₄-Chabazite to form Cu-Chabazite orFe-Chabazite. When copper acetate is used, the copper concentration ofthe liquid copper solution used in the copper ion-exchange is inspecific embodiments in the range from about 0.01 to about 0.4 molar,more specifically in the range from about 0.05 to about 0.3 molar, evenmore specifically in the range from about 0.1 to about 0.25 molar, evenmore specifically in the range from about 0.125 to about 0.25 molar,even more specifically in the range from about 0.15 to about 0.225 molarand even more specifically in the range from about 0.2.

According to an embodiment of the present invention, the molecular sievematerial (which may be zeolitic material or non-zeolitic material) ofthe invention is used in a catalytic process. In general, thecompositions and catalytic articles of the invention can be used in anyconceivable catalytic process, wherein processes involving theconversion of at least one organic compound, more specifically oforganic compounds comprising at least one carbon—carbon and/orcarbon—oxygen and/or carbon—nitrogen bond, more specifically of organiccompounds comprising at least one carbon—carbon and/or carbon—oxygenbond, and even more specifically of organic compounds comprising atleast one carbon—carbon bond. In particularly specific embodiments ofthe present invention, compositions and catalytic articles can be usedto catalyze any one or more of methanol-to-olefin (MTO) reactions,ethylene-to-propylene (ETP) reactions, as well as of the co-reaction ofmethanol and ethylene (CME). The processes involve contacting thecompounds with the compositions or catalytic articles according toembodiments of the invention.

According to a further embodiment of the present invention, thecomposition or catalytic article of the present invention can be used ina catalytic process involving the conversion of at least one compoundcomprising at least one nitrogen—oxygen bond. According to one or moreembodiments of the present invention the composition or the catalyticarticle is used in a selective catalytic reduction (SCR) process for theselective reduction of nitrogen oxides NO_(x); for the oxidation of NH₃,in particular for the oxidation of NH₃ slip in diesel systems; for thedecomposition of N₂O. The term nitrogen oxides, NO_(x), as used in thecontext of the present invention designates the oxides of nitrogen,especially dinitrogen oxide (N₂O), nitrogen monoxide (NO), dinitrogentrioxide (N₂O₃), nitrogen dioxide (NO₂), dinitrogen tetroxide (N₂O₄),dinitrogen pentoxide (N₂O₃), nitrogen peroxide (NO₃). According toparticularly specific embodiments of the present invention, thecomposition or catalytic article can be used in a catalytic processinvolving the conversion of at least one compound comprising at leastone nitrogen—oxygen bond comprises Cu and Fe. The process can beaccomplished by contacting the compound with a catalytic articleaccording to an embodiment of the invention.

Therefore, embodiments of the present invention also relate to a methodfor selectively reducing nitrogen oxides NO_(x) by contacting a streamcontaining NO_(x) with a composition or catalytic article according tothe present invention under suitable reducing conditions; to a method ofoxidizing NH₃, in particular of oxidizing NH₃ slip in diesel systems, bycontacting a stream containing NH₃ with a catalyst composition orcatalytic article under suitable oxidizing conditions; to a method ofdecomposing of N₂O by contacting a stream containing N₂O with a catalystcomposition or catalytic article under suitable decompositionconditions; to a method of controlling emissions in Advanced EmissionSystems such as Homogeneous Charge Compression Ignition (HCCl) enginesby contacting an emission stream with a composition or catalytic articleunder suitable conditions; to a fluid catalytic cracking FCC processwherein the composition is employed as additive; to a method ofconverting an organic compound by contacting said compound with thecomposition or catalytic article under suitable conversion conditions;to a “stationary source” process wherein composition or catalyticarticle is employed.

Accordingly, embodiments of the present invention also relates to amethod for selectively reducing nitrogen oxides NO_(x), wherein agaseous stream containing nitrogen oxides NO_(x), specifically alsocontaining ammonia and/urea, is contacted with the composition orcatalytic article according to the present invention, for example, inthe form of a molded catalytic article, specifically as a moldedcatalytic article wherein the washcoat is deposited on a suitablerefractory carrier, still more specifically on a “honeycomb” carrier.

The nitrogen oxides which are reduced using the catalytic articleaccording to embodiments of the present invention may be obtained by anyprocess, e.g. as a waste gas stream. Among others, waste gas streams asobtained in processes for producing adipic acid, nitric acid,hydroxylamine derivatives, caprolactame, glyoxal, methyl-glyoxal,glyoxylic acid or in processes for burning nitrogeneous materials may bementioned.

In specific embodiments, the catalytic article according to embodimentsof the present invention is used as a molded catalyst, still morespecifically as a molded catalyst wherein the washcoat is deposited on asuitable refractory carrier, still more specifically on a “honeycomb”carrier, for the selective reduction of nitrogen oxides NO_(x), i.e. forselective catalytic reduction of nitrogen oxides. In particular, theselective reduction of nitrogen oxides wherein catalytic articleaccording to an embodiment of the present invention is employed in anexhaust gas stream in the presence ammonia or urea. While ammonia is thereducing agent of choice for stationary power plants, urea is thereducing agent of choice for mobile SCR systems. Typically, the SCRsystem is integrated in the engine and vehicle design and, alsotypically, contains the following main components: SCR catalytic articleincluding the washcoat containing both the copper promoted molecularsieve material and the iron-promoted molecular sieve: a urea storagetank; a urea pump; a urea dosing system; a urea injector/nozzle; and arespective control unit.

More specific embodiments pertain to the use of a composition orcatalytic article for removal of nitrogen oxides NO_(x) from exhaustgases of internal combustion engines, in particular diesel engines,which operate at combustion conditions with air in excess of thatrequired for stoichiometric combustion, i.e. in a lean operation mode.

Therefore, embodiments the present invention also relates to a methodfor removing nitrogen oxides NO_(x) from exhaust gases of internalcombustion engines, in particular diesel engines, which operate atcombustion conditions with air in excess of that required forstoichiometric combustion, i.e., at lean conditions, wherein acomposition or catalytic article described herein is employed ascatalytically active material.

The invention is now described with reference to the following examples.Before describing several exemplary embodiments of the invention, it isto be understood that the invention is not limited to the details ofconstruction or process steps set forth in the following description.The invention is capable of other embodiments and of being practiced orbeing carried out in various ways.

EXAMPLES Example 1 Preparation of Catalyst Compostions and Articles(Cu-CHA)

A Cu-CHA powder catalyst was prepared by mixing 100 g of Na-form CHA,having a silica/alumina mole ratio of 30, with 400 mL of a copper (II)acetate solution of about 1.0 M. The pH was adjusted to about 3.5 withnitric acid. An ion-exchange reaction between the Na-form CHA and thecopper ions was carried out by agitating the slurry at about 80° C. forabout 1 hour. The resulting mixture was then filtered to provide afilter cake, and the filter cake was washed with deionized water inthree portions until the filtrate was clear and colorless, and thewashed sample was dried.

The obtained Cu-CHA catalyst comprised CuO at a range of about 2 to 3.5%by weight, as determined by ICP analysis. A CuCHA slurry was prepared to40% target solids. The slurry was milled and a binder of zirconiumacetate in dilute acetic acid (containing 30% ZrO₂) was added into theslurry with agitation.

The slurry was coated onto 11″D×3″L cellular ceramic cores, having acell density of 400 cpsi (cells per square inch) and a wall thickness of6 mil. The coated cores were dried at 110° C. for 3 hours and calcinedat about 450° C. for 1 hour. The coating process was repeated once toobtain a target washcoat loading of in the range of 2-3 g/in³.

Example 2 Preparation of Ba—Cu-CHA

Ba—Cu-CHA is prepared by drop-wise addition of Ba2+ salt solution intoan aqueous slurry of Cu-CHA prepared in accordance with Example 1. TheCu-CHA filter cake obtained in Example 1 was crushed and then calcinedat 600° C. for 4 h. An aqueous slurry was then prepared to 45% targetsolids, followed by addition of 5% ZrOAc binder, based on the zeolitesolids. The mixture was mixed well, and then was milled. A solution ofBa(OAc)₂ (30 mL, 0.00822 g per gram of zeolite for 0.5 wt % BaO loading)was added dropwise to the aqueous slurry with stirring. The pH wasadjusted to 4.5 using 15% ammonium hydroxide solution. The slurry wasrolled overnight (for at least 12 hours) for in-situ ion exchange ofBa²⁺.

Example 3 Preparation of Fe-CHA

Iron is incorporated into the sodium CHA through Fe-ion exchange at 60°C. for 2 hours at pH 4. The mixture is then washed with deionized water,filtered, and vacuum/air dried. A slurry is prepared of Fe-CHA to 45%target solids, and 5% ZrOAc binder is added based on the zeolite solids.The slurry is mixed well and then milled to D₉₀% of 7-10 microns.

Example 4 Preparation of Washcoat Containing Fe-CHA+Cu-CHA andFe-CHA+Ba—Cu-CHA

The Fe-CHA slurry is then added to the Ba—Cu-CHA slurry in a ratio of2:1 Cu-CHA:Fe-CHA. Similarly, a second sample is made by adding Fe-CHAslurry to Cu-CHA slurry in a ratio of 2:1 Cu-CHA:Fe-CHA. The slurriesare mixed well, and the pH is adjusted to 4.5 with 15% ammoniumhydroxide solution. The mixture is then coated onto to substrates to awashcoat loading of 3 g/in³. The washcoat is dried under air at 130° C.for 5 min. A second coat is then applied. After the final coating, thesubstrate is calcined at 450° C. for 1 hour.

Example 5A and 5B Fe-CHa and Cu-CHA Washcoat

A blended washcoat was prepared by mixing the washcoat of Examples 1 and3 in a ratio of Cu-CHA to Fe-CIA of 2:1 to provide a homogeneouswashcoat mixture. This sample was designated 5A. Sample 58 comprised a511 homogeneous blend of Cu-CHA to Fe-CHA.

Reference Examples

A blended washcoat was prepared by mixing the washcoat of Example 1 andFe-MFI (4 wt % Fe, SAR 27) in a ratio of Cu-CHA to Fe-MFI of 2:1 toprovide a homogeneous washcoat mixture.

A layered washcoat was prepared on a core sample described above in 2:1weight ratios of Cu-CHA to Fe-CHA prepared in accordance with Examples 1and 3 above. Two zoned samples were prepared by placing Cu-CHA in afront zone and Fe-CHA in a rear zone at a ratio of 2:1 Cu-CHA to Fe-CHA.Another zoned sample was prepared in the reverse configuration, withFe-CHA in the front zone and at ratio of 2:1 Cu-CHA to Fe-CHA.

Example 6 Testing

Nitrogen oxides selective catalytic reduction (SCR) efficiency andselectivity of a fresh catalyst core was measured by adding a feed gasmixture of 500 ppm of NO, 500 ppm of NH₃, 10% O₂, 5% 1120, balanced withN₂ to a steady state reactor containing a 1″D×3″L catalyst core. Thereaction was carried at a space velocity of 80,000 hr⁻¹ across a 150° C.to 460° C. temperature range.

The samples were hydrothermally aged in the presence of 10% H₂O at 750°C. for 15 hours, followed by measurement of the nitrogen oxides SCRefficiency and selectivity by the same process as outlined above for theSCR evaluation on a fresh catalyst core.

FIG. 1 shows the NO_(x) conversion versus temperature for the samples,which shows that the uniform mixture of Cu-CHA+Fe-CHA exhibited the bestperformance. As noted above, all mixture/layered/zoned combinations wereprepared with 2:1 ratios of Cu-CHA:Fe-CHA. However, the uniform mixtureclearly outperformed all other samples at 200° C. and 600° C. for NOxconversion.

Example 7 Further Engine Testing

Steady state SCR-test of aged samples were tested on an engine bench(Diamler OM642 3L 6 cylinder engine) with following Diesel OxidationCatalyst (DOC) and Catalytic Soot Filter (CSF) upstream to SelectiveCatalytic Reduction (SCR) catalysts: DOC: 120 g/ft³ platinum groupmetal, Pt/Pd=1/1, 5.66×3″ 400/6; CSF: 39 g/ft³ of Pt and Pd in a Pt/Pdratio of 3/1, 5.66×6″. The data from steady state testing is shown inthe Table and FIG. 1 below. Samples were aged using oven aging: 15h/750° C. hydrothermal. In the table below, “steady state” refers tothere being no restriction on ammonia slip.

In the Table below, NOx efficiency was compared against a sample ofCu-CHA. In the table, the values show the percentage increase ordecrease in NOx conversion at a given condition compared to Cu-CHA.Thus, for example, Example 5 showed 3% better NOx conversion for Run 1,6% better NOx conversion for Run 2, 3% better NOx conversion than Run 3and 10% better NOx conversion for Run 4 than Example 1. The two smallpore zeolites in a homogenous washcoat showed much better NOxconversions for every run compared to Cu-CHA alone or a mixture ofCu-CHA with Fe-MFI.

Run 1 Run 2 Run 3 Run 4 NO_(x) Eff. NO_(x) Eff. NO_(x) Eff. NO_(x) Eff.230° C. @ 230° C. 230° C. 580° C. 0.5 g/L 10 ppm Max. (steady Max.(steady SAMPLE NH₃ NH₃ slip state) state) A: Cu-CHA 0 0 0 0 B: Cu-CHA ++3 +6 +3 +10 Fe-CHA C: Ba-Cu-CHa + +3 +7 +4 +10 Fe-CHA DCu-CHA + −6 −10−14 +1 Fe-MFI)

Ammonia slip was measured and Ba—Cu-CHA+Fe-CHA uniform mixture sampleshows the lowest NH₃ slip compared to other samples at 230° C. Thus, acomposition containing a Fe-promoted 8-ring small pore molecular sieveand a Cu-promoted 8-ring small pore molecular sieve provide optimalperformance at significantly lower NH₃ filling level versus Cu-SSZ13 andthe other samples, which will provide excellent performance for LDD andother light duty lean burn engines.

Example 8 Additional Engine Testing

Example 5A was subjected to HDD FTP testing on a Cummins 2008 300HP ISCengine with catalyst system composed of DOC, CSF, SCRs, and AMOXcatalysts. FIG. 2 shows the catalyst system configuration used in thisHDD FTP engine test. Evaluations were completed over nine consecutiveFTP cycles (Cycles 1 and 2 were stabilization cycles used to establishequilibrium. Cycles 3 through 5 were equilibrium cycles to assessequilibrium performance. Cycle 6 was active cycle with 550° C. peaktemperature. Cycles 7 through 9 were recovery cycles to assessperformance recovery after high temperature exposure, similar to SCRinlet temperature after an active filter regeneration to burn soot.)FIG. 3 shows the temperature profile inlet to SCR1 for all FTP cycles.Urea injection was done to maintain NSR=1.0, NH₃ to NOx ratio. TwoCatalytic Soot Filters (CSFs) with different Pt/Pd ratios (10.1 and 4:1)at 5 g/f³ total PGM loading were used upstream of SCR catalysts togenerate two different NO₂/NOx ratios (0.456 with 10:1 and 0.285 with4:1) in the exhaust feed during testing. FIG. 4 shows the temperatureprofile inlet to SCR1 when test is done with soaks (a cool down step, to160° C., is applied before each cycle) and without soaks. Prior art SCR1and SCR2 were two different copper chabazite catalysts that did notcontain a second 8-ring small pore molecular sieve promoted with iron.Degreening was done for 2 hours/650° C. with active regeneration. Agingwas done by 100 hours/650° C. active regeneration with urea injection.

FIG. 5 is a bar chart showing engine data, equilibrium FTP cycles #3-5,of NOx conversion and N₂O make for fresh samples of Example 5A with nosoaks and fresh prior art SCR1. For each sample in FIGS. 5 through 8,the left bar is the NO_(x) conversion and the right bar is the outletN₂O. FIG. 6 is a bar chart showing engine data, equilibrium FTP cycles#3-5, of NOx conversion and N₂O make for aged samples of Example 5A withno soaks and aged fresh prior art SCR1. FIG. 7 is a bar chart showingengine data, equilibrium FTP cycles #3-5, of NOx conversion and N₂O makefor fresh samples of Example 5A with soaks and fresh prior art SCR1.FIG. 8 is a bar chart showing engine data, equilibrium FTP cycles #3-5,of NOx conversion and N₂O make for aged samples of Example 5A with soaksand aged prior art SCR1. FIG. 9 is a bar chart showing engine data, NOxconversion, of FTP cycles #3-9 of fresh samples of Example 5A with nosoaks and NO2/NOx of 0.5 and fresh prior art SCR2. FIG. 10 is a barchart showing engine data, NOx conversion, of FTP cycles #3-9 of agedsamples of Example 5A with no soaks and NO2/NOx of 0.5 and aged priorart SCR2. FIG. 1 is a bar chart showing engine data, brake specific N2Omake, of FTP cycles #3-9 of fresh samples of Example 5A with no soaksand NO2/NOx of 0.5 and fresh prior art SCR2. FIG. 12 is a bar chartshowing engine data, brake specific N2O make, of FTP cycles #3-9 of agedsamples of Example 5A with no soaks and NO2/NOx of 0.5 and aged priorart SCR2. All NOx conversion values are expressed in percentage (%) andN2O make is expressed in gram per brake horsepower hour (g/bhph).

Based on the HDD FTP engine test data, the SCR performance, NOxconversion, of fresh prior art and Example 5A are comparable forequilibrium FTP cycles 3 through 5 with and without soaks (FIGS. 5 and7). Similarly, NOx conversion, of aged prior art and Example 5A arecomparable for equilibrium FTP cycles 3 through 5 with and without soaks(FIGS. 6 and 8). In general, no soaks condition results in higherperformance versus with soaks testing. Also, higher NO₂ concentration inthe gas feed generates more N₂O (FIGS. 5 through 8). However, Example 5Acatalyst produces significantly lower N₂O both at high and low NO₂/NOxlevels vs. prior art catalyst (FIGS. 5 through 8, 11, and 12). In hotactive cycle 6, performance improvement of Example 5A is apparent,degreened +9% and aged +3%, versus prior art SCR2 (FIGS. 9 and 10). Inrecovery cycles 7-9, Example 5A degreened and aged samples consistentlyshow improved performance versus prior an SCR2 (FIGS. 9 and 10). In allcycles and as Fresh and Aged, Example 5A has lower N₂O make versus priorart SCR1 and SCR2 (FIGS. 5 through 8, 11, and 12).

Reference throughout this specification to “one embodiment,” “certainembodiments,” “one or more embodiments” or “an embodiment” means that aparticular feature, structure, material, or characteristic described inconnection with the embodiment is included in at least one embodiment ofthe invention. Thus, the appearances of the phrases such as “in one ormore embodiments,” “in certain embodiments,” “in one embodiment” or “inan embodiment” in various places throughout this specification are notnecessarily referring to the same embodiment of the invention.Furthermore, the particular features, structures, materials, orcharacteristics may be combined in any suitable manner in one or moreembodiments.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It will be apparent to those skilled in the art thatvarious modifications and variations can be made to the method andapparatus of the present invention without departing from the spirit andscope of the invention. Thus, it is intended that the present inventioninclude modifications and variations that are within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A selective catalytic reduction articlecomprising a washcoat containing both a first 8-ring small poremolecular sieve promoted with copper and a second 8-ring small poremolecular sieve promoted with iron, the catalyst effective to catalyzethe reduction of nitrogen oxides in the presence of a reductant.
 2. Thearticle of claim 1, wherein the first and second 8-ring small poremolecular sieves are selected from the group consisting ofcopper-promoted zeolite having a structure type selected from AEI, AFT,AFX, CHA, EAB, ERI, KFI, LEV, SAS, SAT, and SAV.
 3. The article of claim2, wherein the first and second 8-ring small pore molecular sieves havethe CHA crystal structure.
 4. The article of claim 2, wherein the 8-ringsmall pore molecular sieve having the CHA crystal structure is selectedfrom an aluminosilicate zeolite, a borosilicate, a gallosilicate, aSAPO, an AlPO, a MeAPSO, and a MeAPO.
 5. The article of claim 3, whereinthe 8-ring small pore molecular sieve is selected from the groupconsisting of SSZ-13, SSZ-62, natural chabazite, zeolite K-G, Linde D,Linde R, LZ-218, LZ-235, LZ-236, ZK-14, SAPO-34, SAPO-44, SAPO-47, andZYT-6.
 6. The article of claim 1, wherein the first 8-ring small poremolecular sieve promoted with copper further comprises a bariumcomponent.
 7. The article of claim 1, wherein the washcoat layer isdisposed on a substrate.
 8. The article of claim 1, wherein first 8-ringsmall pore molecular sieve promoted with copper and the second 8-ringsmall pore molecular sieve promoted with copper are present in a ratioin the range of 1:1 to 10:1 of the first 8-ring small pore molecularsieve material to the second 8-ring small pore molecular sieve.
 9. Thearticle of claim 1, wherein the first 8-ring small pore molecular sieveand second 8-ring small pore molecular sieve each are selected fromSSZ-13 and SSZ-62 and are present in a ratio in the range of 1:1 to 10:1of the copper-promoted 8-ring small pore molecular sieve to theiron-promoted 8-ring small pore molecular sieve.
 10. The article ofclaim 9, wherein the first 8-ring small pore molecular sieve furthercomprises a barium component.
 11. The article of claim 1, wherein thecatalyst is effective to catalyze the selective catalytic reduction ofnitrogen oxides in the presence of a reductant at temperatures between200° C. and 600° C.
 12. The article of claim 3, wherein zeolite has asilica to alumina ratio is in the range of 20 and
 50. 13. A method forselectively reducing nitrogen oxides (NO_(x)), the method comprisingcontacting an exhaust gas stream containing NO_(x) with a selectivecatalytic reduction catalytic article comprising a washcoat containing afirst 8-ring small pore molecular sieve promoted with copper and asecond 8-ring small pore molecular sieve promoted with iron.
 14. Themethod of claim 13, wherein the first and second 8-ring small poremolecular sieves are selected from the group consisting of AEI, AFT,AFX, CHA, EAB, ERI, KFI, LEV, SAS, SAT, and SAV.
 15. The method of claim14, wherein the first and second 8-ring small pore molecular sieves havethe CHA crystal structure and is selected from the group consisting ofaluminosilicate zeolite, SAPO, AlPO, and MeAPO.
 16. The method of claim15, wherein first and second 8-ring small pore molecular sieves havingthe CHA crystal structure are selected from the group consisting ofSSZ-13, SSZ-62, natural chabazite, zeolite K-G, Linde D, Linde R,LZ-218, LZ-235, LZ-236, ZK-14, SAPO-34, SAPO-44, SAPO-47, and ZYT-6. 17.The method of claim 16, wherein the first 8-ring small pore molecularsieve having the CHA crystal structure is an aluminosilicate zeolite.18. The method of claim 17, wherein the aluminosilicate zeolite isselected from SSZ-13 and SSZ-62.
 19. The method of claim 13, whereinsecond 8-ring small pore molecular sieve is selected from the groupconsisting of AEI, AFT, AFX, CHA, EAB, ERI, KFI, LEV, SAS, SAT, and SAV.20. The method of claim 19, wherein the second 8-ring small poremolecular sieve has the CHA crystal structure and is selected from thegroup consisting of SSZ-13, SSZ-62, natural chabazite, zeolite K-G,Linde D, Linde R, LZ-218, LZ-235, LZ-236, ZK-14, SAPO-34, SAPO-44,SAPO-47, and ZYT-6.